Well the plastic is painted, obviously in some way. The MBP is silver, that can peel off. Several people here have reports on that, even after short use. On the MB the glossyness disappears in areas and it looks like the unit has been scratched by a screwdriver or something, although it has been taken care off like a baby.
And sorry, but I am not customer supporter for those friends - if they want to take it to Apple I'll let them decide, but my guess is that Apple will just blame it on wear and tear.
Are you claiming the MBP is painted silver or something? That's the first I've heard of it. Pretty sure it's all metal. Which parts of it have paint on it? Can you point to some of these reports?
Regarding the MacBook, it's hard to say without seeing it.
I have a hard time seeing how it could look like it was scratched by a screwdriver and worn down if it was taken care of like a baby though.